21289979 has 4 divisors (see below), whose sum is σ = 21307440. Its totient is φ = 21272520.

The previous prime is 21289969. The next prime is 21289981. The reversal of 21289979 is 97998212.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21289979 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21289949) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6752 + ... + 9389.

It is an arithmetic number, because the mean of its divisors is an integer number (5326860).

Almost surely, 2^21289979 is an apocalyptic number.

21289979 is a deficient number, since it is larger than the sum of its proper divisors (17461).

21289979 is a wasteful number, since it uses less digits than its factorization.

21289979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17460.

The product of its digits is 163296, while the sum is 47.

The square root of 21289979 is about 4614.1065223941. The cubic root of 21289979 is about 277.1565059780.

The spelling of 21289979 in words is "twenty-one million, two hundred eighty-nine thousand, nine hundred seventy-nine".